1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to encoding and decoding an audio signal, and more particularly, to encoding or decoding an audio signal by adaptively interpolating a linear predictive coding (LPC) coefficient depending on whether a transient signal is present in an audio signal in a current frame.
2. Description of the Related Art
In general, an audio signal is processed in units of predetermined time units which are referred to as frames. In case of processing the audio signal in units of frames, a discontinuous point is generated between adjacent frames due to a quantization error and so on, thus deteriorating audio quality. Thus, various algorithms have been proposed in order to prevent adjacent frames from being discontinuous. In the case of LPC, an LPC coefficients of adjacent frames are interpolated in order to prevent audio quality from deteriorating due to a sudden change in LPC coefficients.
Interpolation is performed on the LPC coefficients in order to prevent a change in a source model obtained by analyzing an input audio signal. The interpolation is performed by detecting a change in the trace of poles on a Z-domain in which the LPC coefficients are present. In general, an LPC coefficient is interpolated using line spectral frequency (LSF) transformation or line spectral pair (LSP) transformation.
FIGS. 1A and 1B are reference diagrams for explaining the problem of a related art method of interpolating an LPC coefficient. Referring to FIGS. 1A and 1B, if there is a transient signal that suddenly changes the magnitude of an input audio signal, a signal reconstructed by interpolating an LPC coefficient causes pre-echo. Pre-echo is noise occurring when a previous small-magnitude signal is affected by a large-magnitude signal in the end of a transient section.
Accordingly, a related art method of interpolating an LPC coefficient is disadvantageous in that a change in an LPC coefficient in a transient section increases an error, thus causing noise.